How do you account for the large scale enterprise in the late nineteenth century?

So are you just asking why businesses got to be so big in
the late 1800s?  If so, the main reason is
technology.

Before the civil War, especially, it was very
difficult to make a really large business.  There were not that many large machines that
could produce goods on a large scale.  Even if there had been, there were not any huge
markets, tied together by railroads, that could consume all the goods.  The lack of
railroads also made it much harder for factories in one area to get raw materials from
another area.  It was much more necessary to have smaller factories spread around the
country.

As the 1800s went along, the boom in railroad tied
markets together much more efficiently.  Along with this came technological improvements
that made larger machines possible.  In addition, things like the telegraph made
communications between parts of a large company much more
possible.

Because of all these technological changes, large
scale enterprise became much more prevalent in the late 1800s.